1. FIELD OF THE INVENTION
The present invention relates to an ink jet apparatus. In this specification, it should be construed that a word "recording" involves a technical concept of applying ink to a various kind of ink receiving medium such as cloth, thread, paper, sheet-like material and so forth each adapted to receive ink thereon to be printed, and that words "a recording apparatus" involve a technical concept defined by various kinds of information processing systems or a printer serving as an outputting system for each of the information processing system. The present invention can be applied to each of the information processing system and the printer as mentioned above
2. DESCRIPTION OF THE RELATED ART
A recording apparatus such as a printer, a copying machine, a facsimile or the like, or a recording apparatus usable as an outputting system for a composite type electronic system or a work station inclusive of a computer, a word processor or the like is constructed such that an image is recorded on a recording material (recording medium) such as a paper, a plastic sheet or the like based on given image information. An ink jet recording process for enabling each recording operation to be achieved with a high quality of recorded image at a high speed is employed in a recording apparatus of the foregoing type.
Generally, an ink jet apparatus includes an ink jet head which is substantially composed of a plurality of ink discharge openings arranged in the row-shaped pattern on a discharge opening surface, a common ink chamber communicated with the ink feeding ports for feeding ink to the ink discharge openings, and a tank portion having an ink feeding port formed thereon for feeding ink to the common ink chamber through the ink feeding port.
With respect to the ink jet apparatus including the ink jet head constructed in that way, there sometimes arises a malfunction that the viscosity of ink is increased due to evaporation of volatile components in ink through the ink discharge openings induced by the dry atmosphere or a similar factor while any recording operation is not performed with the ink jet apparatus with the result that merely incorrect ink discharge is achieved or any ink discharge can not be achieved with the ink jet apparatus. In this case, since it becomes difficult that ink is discharged from respective discharge openings, there arises another malfunction that a quality of recorded image is degraded.
To cope with the aforementioned malfunctions, discharge recovering treatment has been hitherto periodically conducted for the ink jet head irrespective of whether or not a recording operation is performed with the ink jet apparatus. In practice, an discharge recovering treatment unit substantially composed of a cap member for forming a closed space inclusive of a discharge opening plane while coming in tight contact with the discharge opening plane defined by a plurality of ink discharge openings of the ink jet head, a suction pump fitted to the cap member for bringing the closed space in the negative pressure state, and ink discharge openings for discharging ink discharged in the closed space by the suction force generated by the suction pump is used in order to conduct the foregoing type of discharge recovering treatment.
To facilitate understanding of the present invention, a typical conventional ink jet apparatus will be described below mainly in respect of a structure and a mode of operation of each of an ink jet head and an discharge recovering treatment unit with reference to FIG. 12 and FIG. 13.
FIG. 12 is a fragmentary sectional view of the conventional ink jet apparatus, showing the opened state that a capping unit is parted away from an ink jet head, and FIG. 13 is a fragmentary sectional view of the conventional ink jet apparatus similar to FIG. 12, showing the closed state that the capping unit is brought in tight contact with the ink jet head. Referring to FIG. 12, an ink jet head 1 is held in such a manner as to move in the direction perpendicular to the plane of the drawing with the aid of a moving mechanism and a holding mechanism each of which is not shown in the drawing. The ink jet head 1 includes a tank portion 1a in which ink Ik is fed by actuating a certain mechanism (not shown) so as to allow a certain amount of ink Ik to be storably received therein.
An ink feeding port 1b is arranged at the central part on the lower wall of the tank portion 1a so that the tank portion 1a is communicated with a common ink chamber 1c to be described later via the ink feeding port 1b. The common ink chamber 1c is located below the tank portion 1a. The common ink chamber 1c serve as an ink tank storing portion for feeding ink Tk in the tank portion 1a to all of ink discharge openings. In FIG. 12, reference numeral 1d designates a discharge opening plane which is defined by all the ink discharge openings, and reference numeral 1e designates a discharge opening group which is located in the vicinity of the ink feeding port 1b. The discharge opening group 1c is located at the central part as viewed from the standpoint of the whole ink discharge openings. In addition, reference numerals 1f and 1g designate discharge opening groups each of which is parted away from the ink feeding port 1b. Each of the discharge opening groups 1f and 1g is located at the end edge part as viewed from the standpoint of the whole ink discharge openings.
A peripheral wall portion 2b is formed along the peripheral edge portion of an upper surface 2a of a cap 2 serving as capping means in order to assure that a discharge opening plane 1d of the ink jet head 1 is thrusted by the peripheral wall portion 2b of the cap 2 along the whole peripheral edge thereof after the cap 2 is raised up by actuating a movable mechanism to be described later so as to come in tight contact with the discharge opening plane 1d of the ink jet head 1. The peripheral wall portion 2b of the cap 2 adapted to come in contact with the ink jet head 1 is molded of an elastic material such as a rubber or a similar material in consideration of conditions such as absorption of shock arising at the time of coming in contact with the ink jet head 1, improvement of the contact state after the foregoing time and so forth.
An ink suction port 2c is formed at the central part of the upper surface 2a of the cap 2, and an ink suction pipe 2d suspends from the ink suction port 2c. The lower end of the ink suction pipe 2d is connected to a suction pump 4 via a pipe 3 extending therebetween.
The cap 2 is held by a holder 5 capable of being displaced in the upward/downward direction with the aid of the movable mechanism (not shown). With this construction, it is possible to bring the cap 2 in tight contact with the discharge opening plane 1d of the ink jet head 1 or release the cap 2 from the tight contact state by actuating the movable mechanism.
In addition, an ink absorbing member 6 for absorbing ink Ik therein is placed on the upper surface 2a of the cap 2.
Next, a mode of suction recovering operation of the conventional ink jet apparatus constructed in that way will be described below.
First, as shown in FIG. 12, the ink jet head 1 is displaced to a home position by actuating a driving mechanism (not shown) so that the discharge opening plane 1d of the ink jet head 1 faces to the upper surface 2a of the cap 2 in the spaced relationship. Subsequently, the holder 5 is displaced in the upward direction by actuating the movable mechanism (not shown) so that the peripheral wall portion 2b of the cap 2 held on the holder 5 is brought in tight contact with the discharge opening plane 1d of the ink jet head 1 along the peripheral edge of the latter with a certain intensity of thrusting force, whereby the space in front of the discharge opening plane 1d of the ink jet head 1 becomes a closed space. When the suction pump 4 is driven, the pressure in the closed space becomes negative pressure. Thus, ink Ik in the tank portion 1a is sucked through the respective ink suction ports, causing ink having an increased viscosity and gas bubbles remaining in the respective ink suction ports and the common ink chamber 1c to be removably dislocated into the interior of the closed space. At the same time, ink Ik kept in the normal state is filled in the respective ink discharge openings from the common ink chamber 1c. As ink Ik is introduced into the closed space, it is absorbed in the ink absorbing member 6. Thereafter, ink Ik is displaced in the downward direction through the ink absorbing member 6, and finally, it is collected in a tank (not shown) via the ink suction pipe 2d and the pipe 3.
Next, after the closed space is released from the negative pressure state by actuating a negative pressure releasing mechanism such as a stop valve or the like (not shown) fitted to the cap 2, the driving of the suction pump 4 is interrupted, causing the holder 5 to be lowered until the cap 2 is parted away from the discharge opening plane 1d of the ink jet head 1, whereby a series of suction recovering operations are completed. It should be noted that the ink absorbing member is not shown in FIG. 13 for the purpose of simplification of illustration.
However, the conventional ink jet apparatus constructed in the above-described manner has the following drawback. Specifically, since the ink feeding port 1b of the ink jet head 1 and the ink suction port 2c of the cap 2 face to each other in the upward/downward direction, a manner of allowing Ink to flow through respective discharge openings at the central part of a row of ink discharge openings is different from that of allowing ink to flow through respective discharge openings at the peripheral part of a row of ink discharge openings. For this reason, an excellent quality of recorded image can not be maintained because the suction recovering state differs depending on the position occupied by each discharge opening group.
In more detail, as shown in FIG. 13, since ink remaining in the vicinity of the central discharge opening group 1e among a group of ink discharge openings is located around the line extending between the ink feeding port 1b and the ink suction port 2c, it is largely affected by a high intensity of sucking force. At this time, since the pressure loss induced by the ink absorbing member 6 interposed between the ink jet head 1 and the cap 2 is small, ink smoothly flows in the closed space at a high speed in the P arrow-marked direction as seen in the drawing, resulting in ink having an increased density and gas bubbles remaining in the discharge opening group 1e being removably dislocated from the latter at a high efficiency. On the contrary, since ink remaining in the vicinity of each of discharge opening groups if and 1g located along the end edge of a group of ink discharge openings is parted away from the line extending between the ink feeding port 1b and the ink suction port 2c, it is not largely affected by the suction force, and moreover, the pressure loss is relatively increased due to the presence of the ink absorbing member 6, ink slowly flows at a low speed in the R arrow-marked direction, resulting in ink having an increased viscosity and gas bubbles remaining in respective discharge openings in the discharge opening groups 1f and 1g failing to be removably dislocated to a sufficient extent.
As is apparent from the above description, as far as the conventional ink jet apparatus constructed in that way is concerned, uniform discharging properties can not be recovered with the whole discharge opening groups no matter how discharge recovering treatment is conducted for a group of ink discharge openings. This leads to the result that a density of recorded image fluctuates over the whole area of the latter, an moreover, and ink discharge is incorrectly achieved with the conventional ink jet apparatus, resulting in each recording operation being achieved at a high level of quality only with much difficulties. Especially, when the number of discharge openings is increased, the aforementioned malfunctions can remarkably be recognized.